Swarms of bees seeking new nests make decisions using a system that's very …

The human brain is wonderfully complex. Within it, there are billions of neurons, each collecting information and determining whether to respond to it. In some cases, groups of neurons compete for an outcome; when a group reaches a certain level of activity, its output ends up being chosen. To help make their case, these neurons can send positive signals to each other, and they can inhibit others with different agendas. Ideally, this system improves the chances of reaching an optimal decision; it’s an elegant way to make sense of lots of competing input.

As if we didn't think bees were cool enough already, Science reports this week that this approach to decision making is echoed in the behavior of honeybee swarms. Just as our neurons emit inhibitory signals, bees can hinder other hivemates that are advocating a different course of action. As with neurons, the swarm’s collective decision is made when a particular threshold is reached. But, unlike neurons, the bees have a very physical means of inhibiting those with a competing message: they headbutt them.

When a group of honeybees are ready to create a new colony, thousands of bees, along with one queen, set off from their old hive. Scout bees are faced with the task of finding a suitable nest and reporting back to their group with the location of the best nest site; the information is communicated via the famous waggle dance. Unfortunately, the scouts don’t always agree on which site is best. So how does a swarm decide where to relocate?

A group of researchers found that, upon returning to the swarm, scout bees will "headbutt" other scouts that are promoting a different nest site. This headbutt transfers a vibrational signal that, when repeated enough times, causes the other bee to stop dancing. Once a certain threshold is reached—that is, enough scouts that were advocating alternative sites have been headbutted into submission—the decision is made, and the swarm will move to the winning nest site.

The researchers created an analytic model based on differential equations, taking into account the interaction rules they learned by observing swarming bees. The model suggested that this type of cross inhibition is often necessary in order for the swarms to reach a decision. Without inhibitory signals, bees may be able to "induce" some bees to switch sides, but it's likely that enough bees will switch sides to keep the swarm from entering a stable deadlock. The use of inhibitory signals, as well as a threshold, ensures that a decision will be reached and the swarm will be in agreement as it lifts off to colonize a new nest.

While a honeybee swarm and the human brain have some aspects in common, they’re from such distinct evolutionary paths that the degree of similarity between their strategies is pretty incredible. Clearly, this type of system is a particularly effective way to make a decision that has to incorporate multiple sources of biological information.

Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida

add: maybe if the bees made decisions by getting beaten over the head with the largest bag of money...

In the case of Congress, too much head-butting has likely led to Traumatic Brain Injuries (TBIs). The report I saw said that "Repeated mild brain injuries occurring over an extended period (i.e., months or years can result in cumulative neurologic and cognitive deficits, but repeated mild brain injuries occurring within a short period (i.e., hours, days, weeks) can be catastrophic or fatal".

I think in the case of Congress, we may have some cognitive deficits happening in response to an activity to which bees are immune.

It seems more likely that the boss will have other works (and management) headbutt you until you stop dissenting. If at some point the amount of dissenters becomes the majority, ie: there's enough people wanting a raise that you headbutt the opponents down, then a decision will be reached to give everyone a raise!

An interesting thing about the congress example is that this system doesn't really work with only two bees.

Since the bees all have the same evolutionary interest in the outcome the anthromorphization of this result--while admittedly amusing--is kind of unfortunate because it masks the quite wonderful point of how weirdly alien this behaviour is to humans.

Despite its physical nature, this is a communication mechanism, not a dominance mechanism. Bees don't get butted into submission, they get signaled into silence.

Dominance/submission terminology only makes sense in the context of hierarchical social organisms engaged in mate competition, which bees are not.

So head-butting gets everyone on the same page, but does it in any way help the swarm pick the best site (if there are criteria for that).

As for the human brain - well science is cool and everything - but evolution is pretty conservative and seems to like to use the same methods to solve problems over and over...so...just sayin'.

Well, what's interesting is that the human brain and bees' method of communication have evolved totally separately. So the usual conservative mechanisms of evolution don't really play into effect.

That said, biology in general seems to repeat itself over and over when it comes to 'decision making', and this is more evidence along those lines, which is really cool. There is something satisfying about the fact that evolution tends to find the same kind of solutions to the same kind of problems over and over in otherwise quite different contexts.

And to elaborate, decision making in biological systems often shows up as stochastic switches, which is not surprising given how noisy the signaling environment is in any biological system.

Isn't this how most wars and civil conflicts (systems of integrating multiple complex variables and factors into a hopefully decisive result) are resolved?

The interesting thing (as I understand from reading the paper, but I am not a scientist so caveat emptor) is: a system in which individual bees "induce each other to change commitment" (i.e., they get each other to change sides) would reach an equilibrium involving equal numbers of bees on each side. When there are more bees favoring one option, the recruitment of those bees speeds up and the numbers equalize. (That's what the article asserts—I haven't worked through the modeling and evidence supporting that claim.)

The only approach that avoids making "equal numbers on both sides" a stable equilibrium is the one that involves delivering a stop signal to opponents, rather than recruiting them to your side.

So recruiting opponents to your side won't work to break up a disagreement. You have to incapacitate your opponents. With extreme prejudice.

I'm trying to understand what you just wrote but I must be missing something because if the majority started headbutting the others, they would end up with absolute dominance - not with a balance against dissenters.

I'm trying to understand what you just wrote but I must be missing something because if the majority started headbutting the others, they would end up with absolute dominance - not with a balance against dissenters.

As I understand it, the headbutting (which incapacitates the other bees) does deliver dominance. Which is good: a decision gets made. The odd thing is, conversion (that is, switching bees to your side) wouldn't deliver dominance; it would just result in balance. From the article:

Quote:

When one site gains a majority of scouts [this is under the model where conversion, not incapacitation, happens], the switching of scouts from it to the other site increases, forcing the system back to a state of equal commitment [Fig. 3A and (18)]. Such stable deadlock is clearly sub-optimal, since it will result in the swarm never achieving a consensus; this could mean the swarm never lifts off.

Once again, IANAS, so if anyone with domain-specific knowledge wants to jump in here I'd love to hear your take.

Bees and human beings do not come from distinct evolutionary paths. Both species accomplish all their behavior with the same two proteins actin and myosin. The appearance of the Eukaryotic cell and later of Metazoan organisms with a bilateral body plan are the two major events in the evolution of complex organisms. Both bees and human beings are downstream from those events.

So head-butting gets everyone on the same page, but does it in any way help the swarm pick the best site (if there are criteria for that).

As for the human brain - well science is cool and everything - but evolution is pretty conservative and seems to like to use the same methods to solve problems over and over...so...just sayin'.

Well, what's interesting is that the human brain and bees' method of communication have evolved totally separately. So the usual conservative mechanisms of evolution don't really play into effect.

That said, biology in general seems to repeat itself over and over when it comes to 'decision making', and this is more evidence along those lines, which is really cool. There is something satisfying about the fact that evolution tends to find the same kind of solutions to the same kind of problems over and over in otherwise quite different contexts.

And to elaborate, decision making in biological systems often shows up as stochastic switches, which is not surprising given how noisy the signaling environment is in any biological system.

That's a bit what I was getting at. Camera eyes are another example, as are compound eyes like in insects and that eldritch aquatic abomination from yesterday's story (I think it's called homoplasy or something like that). Evolution tends to use similar methods to solve the problem. So yeah...science is cool, but I don't know that it is so surprising that a colony of bees and the human brain use similar methods for decision making. Still wondering about whether it ends up in a better decision for the bees.

Bees and human beings do not come from distinct evolutionary paths. Both species accomplish all their behavior with the same two proteins actin and myosin. The appearance of the Eukaryotic cell and later of Metazoan organisms with a bilateral body plan are the two major events in the evolution of complex organisms. Both bees and human beings are downstream from those events.

They come from separate paths with respect to these systems of intercellular communication. Actin and Myosin are for intracellular transport and cytoskeletal movement, so I don't see how this is relevant. Nothing in the shared evolutionary history would suggest that the mechanistic frameworks would be used for the human brain and a 'hive mind' decision making method.

I'm sure my colleagues who work on actin and myosin would agree that they're incredibly important for cellular activity, but they aren't going to be specifically relevant in this context.

xdevnull wrote:

That's a bit what I was getting at. Camera eyes are another example, as are compound eyes like in insects and that eldritch aquatic abomination from yesterday's story (I think it's called homoplasy or something like that). Evolution tends to use similar methods to solve the problem. So yeah...science is cool, but I don't know that it is so surprising that a colony of bees and the human brain use similar methods for decision making. Still wondering about whether it ends up in a better decision for the bees.

Evolution is an optimization mechanism, so in some tautological sense, yeah, this makes "better" decisions for the bees, but that depends on what your comparing against. If this is a widespread mechanism in bees for decision making (and the article suggests it is), then by the metric of "bees survive and increase in population", this works. It's notable that evolution works under a lot of constraints and can only search locally though, so it's quite possible there's a much better solution that evolution can't get to due to some path dependency issues in the solution space.

Also, it's worth noting that "evolution uses similar methods" is an empirical finding, not an a priori expectation. What's surprising is not so much the similar methods issue in and of itself, but rather that it suggests the solution space evolution explores is heavily constrained to cover similar ground even across divergent species. Some of this naturally arises from the fact that there is an overarching issue of noise and stochasticity in biological systems and environments. Still, this implies that there's something deeper going on in the actual logic of the systems, not just similarity at the chemical level. If you accept that the logic is similar for these systems and this implies similar mechanisms, then this isn't surprising, but there's no reason to expect *that* a priori either. Anyway, I think it's a really quite cool result to find, and doubly so when the math actually works out.

Also, looking at the article, this is a time when I really hate Science's page limits. All of the modeling information is stuck in the SI Materials and Methods section.